U.S. patent application number 15/203476 was filed with the patent office on 2016-10-27 for method and device for receiving or transmitting downlink control signal in wireless communication system.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Jihyun LEE, Seungmin LEE, Hanbyul SEO, Inkwon SEO.
Application Number | 20160316460 15/203476 |
Document ID | / |
Family ID | 50341710 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160316460 |
Kind Code |
A1 |
LEE; Jihyun ; et
al. |
October 27, 2016 |
METHOD AND DEVICE FOR RECEIVING OR TRANSMITTING DOWNLINK CONTROL
SIGNAL IN WIRELESS COMMUNICATION SYSTEM
Abstract
A method and a user equipment (UE) for receiving a downlink
control signal in a wireless communication system are discussed.
The method according to an embedment includes determining a minimum
aggregation level for a plurality of enhanced physical downlink
control channel (EPDCCH) candidates. The minimum aggregation level
is 2 if both a downlink (DL) bandwidth includes at least 25
resource blocks (RBs) and a downlink control information (DCI)
format is one of DCI formats 2, 2A, 2B, 2C and 2D. The method
further includes monitoring the plurality of EPDCCH candidates in
an EPDCCH set to decode an EPDCCH transmitted from a base station
(BS) using the minimum aggregation level; and receiving a physical
downlink shared channel (PDSCH) corresponding to the decoded
EPDCCH.
Inventors: |
LEE; Jihyun; (Anyang-si,
KR) ; SEO; Inkwon; (Anyang-si, KR) ; SEO;
Hanbyul; (Anyang-si, KR) ; LEE; Seungmin;
(Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
50341710 |
Appl. No.: |
15/203476 |
Filed: |
July 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14349605 |
Apr 3, 2014 |
9401792 |
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PCT/KR2013/008477 |
Sep 23, 2013 |
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15203476 |
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61723754 |
Nov 7, 2012 |
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61721517 |
Nov 2, 2012 |
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61703792 |
Sep 21, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/001 20130101;
H04L 1/1893 20130101; H04L 5/0053 20130101; H04W 72/042 20130101;
H04W 72/044 20130101; H04W 48/16 20130101; H04L 5/0037 20130101;
H04W 48/12 20130101; H04L 5/0007 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04L 5/00 20060101 H04L005/00 |
Claims
1. A method for receiving a downlink control signal by a user
equipment (UE) in a wireless communication system, the method
comprising: determining a minimum aggregation level for a plurality
of enhanced physical downlink control channel (EPDCCH) candidates,
wherein the minimum aggregation level is 2 if both a downlink (DL)
bandwidth includes at least 25 resource blocks (RBs) and a downlink
control information (DCI) format is one of DCI formats 2, 2A, 2B,
2C and 2D; monitoring the plurality of EPDCCH candidates in an
EPDCCH set to decode an EPDCCH transmitted from a base station (BS)
using the minimum aggregation level; and receiving a physical
downlink shared channel (PDSCH) corresponding to the decoded
EPDCCH.
2. The method according to claim 1, wherein, if a number of
physical resource block (PRB) pairs constituting the EPDCCH set is
4, a number of the EPDCCH candidates is set to 8, 4, 2, and 1 at
aggregation levels 2, 4, 8, and 16, respectively.
3. The method according to claim 1, further comprising: receiving
information regarding the number of EPDCCH candidates for each
aggregation level (L) from the BS.
4. The method according to claim 1, further comprising: if an
aggregation level (L1) is set to be higher than a number of
enhanced control channel elements (ECCEs) contained in the EPDCCH
set, allocating EPDCCH candidates for the L1 to other aggregation
levels.
5. The method according to claim 4, wherein the EPDCCH candidates
for the L1 are attempted to be allocated to the other aggregation
levels with a priority from a highest aggregation level to a lowest
aggregation level from among aggregation levels less than the L1,
from among aggregation levels set in the EPDCCH set.
6. The method according to claim 5, wherein, if an additional
EPDCCH candidate cannot be allocated to a specific aggregation
level from among aggregation levels less than the L1, the
additional EPDCCH candidate is allocated to a next highest
aggregation level subsequent to the specific aggregation level.
7. The method according to claim 1, wherein, a number of EPDCCH
candidates of the EPDCCH set is decided according to each
aggregation level (L), a number (N) of physical resource block
(PRB) pairs of the EPDCCH set, and a number of enhanced control
channel elements (ECCEs) per PRB pair, and wherein a number of
EPDCCH candidates for each N is fixed.
8. The method according to claim 1, wherein, if two EPDCCH sets are
present, the two EPDCCH sets are set to have different minimum
aggregation levels.
9. The method according to claim 1, wherein, if two EPDCCH sets are
present, the two EPDCCH sets are set in a manner that individual
aggregation levels have different numbers of EPDCCH candidates.
10. The method according to claim 9, wherein, if an aggregation
level (L2) higher than a number of enhanced control channel
elements (ECCEs) contained in a first EPDCCH set is set in the
first EPDCCH set, EPDCCH candidates for the L2 are allocated to a
second EPDCCH set.
11. The method according to claim 10, wherein the EPDCCH candidates
for the L2 are attempted to be allocated to the second EPDCCH set
with a priority from a highest aggregation level to a lowest
aggregation level from among aggregation levels less than the L2,
from among aggregation levels set in the first EPDCCH set.
12. The method according to claim 11, wherein, if an additional
EPDCCH candidate cannot be allocated to a specific aggregation
level from among aggregation levels less than the L2, the
additional EPDCCH candidate is allocated to a next highest
aggregation level subsequent to the specific aggregation level.
13. The method according to claim 1, wherein, if an additional
EPDCCH candidate cannot be allocated to a specific aggregation
level from among aggregation levels less than a threshold
aggregation level, the additional EPDCCH candidate is allocated to
a next highest aggregation level subsequent to the specific
aggregation level.
14. The method according to claim 13, wherein the allocating of the
additional EPDCCH candidate to the next highest aggregation level
subsequent to the specific aggregation level is limited by a total
number of enhanced control channel elements (ECCEs), and wherein
the total number of the ECCEs that may be generated is 32.
15. A user equipment (UE) configured to receive a downlink control
signal in a wireless communication system, the UE comprising: a
radio frequency (RF) unit; and a processor configured to control
the RF unit, wherein the processor is further configured to:
determine a minimum aggregation level for a plurality of enhanced
physical downlink control channel (EPDCCH) candidates, wherein the
minimum aggregation level is 2 if both a downlink (DL) bandwidth
includes at least 25 resource blocks (RBs) and a downlink control
information (DCI) format is one of DCI formats 2, 2A, 2B, 2C and
2D, monitor the plurality of EPDCCH candidates in an EPDCCH set to
decode an EPDCCH transmitted from a base station (BS) using the
minimum aggregation level, and receive a physical downlink shared
channel (PDSCH) corresponding to the decoded EPDCCH.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of co-pending U.S. patent
application Ser. No. 14/349,605 filed on Apr. 3, 2014, which is
filed as the National Phase of PCT/KR2013/008477 filed on Sep. 23,
2013, which claims the benefit under 35 U.S.C. .sctn.119(e) to U.S.
Provisional Application No. 61/723,754 filed on Nov. 7, 2012,
61/721,517 filed on Nov. 2, 2012, and 61/703,792 filed on Sep. 21,
2012, all of which are hereby expressly incorporated by reference
into the present application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a wireless communication
system, and more particularly to a method and apparatus for
receiving and transmitting downlink control signal in the wireless
communication system.
[0004] 2. Discussion of the Related Art
[0005] Recently, various devices requiring machine-to-machine (M2M)
communication and high data transfer rate, such as smartphones or
tablet personal computers (PCs), have appeared and come into
widespread use. This has rapidly increased the quantity of data
which needs to be processed in a cellular network. In order to
satisfy such rapidly increasing data throughput, recently, carrier
aggregation (CA) technology which efficiently uses more frequency
bands, cognitive ratio technology, multiple antenna (MIMO)
technology for increasing data capacity in a restricted frequency,
multiple-base-station cooperative technology, etc. have been
highlighted. In addition, communication environments have evolved
such that the density of accessible nodes is increased in the
vicinity of a user equipment (UE). Here, the node includes one or
more antennas and refers to a fixed point capable of
transmitting/receiving radio frequency (RF) signals to/from the
user equipment (UE). A communication system including high-density
nodes may provide a communication service of higher performance to
the UE by cooperation between nodes.
[0006] A multi-node coordinated communication scheme in which a
plurality of nodes communicates with a user equipment (UE) using
the same time-frequency resources has much higher data throughput
than legacy communication scheme in which each node operates as an
independent base station (BS) to communicate with the UE without
cooperation.
[0007] A multi-node system performs coordinated communication using
a plurality of nodes, each of which operates as a base station or
an access point, an antenna, an antenna group, a remote radio head
(RRH), and a remote radio unit (RRU). Unlike the conventional
centralized antenna system in which antennas are concentrated at a
base station (BS), nodes are spaced apart from each other by a
predetermined distance or more in the multi-node system. The nodes
can be managed by one or more base stations or base station
controllers which control operations of the nodes or schedule data
transmitted/received through the nodes. Each node is connected to a
base station or a base station controller which manages the node
through a cable or a dedicated line.
[0008] The multi-node system can be considered as a kind of
Multiple Input Multiple Output (MIMO) system since dispersed nodes
can communicate with a single UE or multiple UEs by simultaneously
transmitting/receiving different data streams. However, since the
multi-node system transmits signals using the dispersed nodes, a
transmission area covered by each antenna is reduced compared to
antennas included in the conventional centralized antenna system.
Accordingly, transmit power required for each antenna to transmit a
signal in the multi-node system can be reduced compared to the
conventional centralized antenna system using MIMO. In addition, a
transmission distance between an antenna and a UE is reduced to
decrease in pathloss and enable rapid data transmission in the
multi-node system. This can improve transmission capacity and power
efficiency of a cellular system and meet communication performance
having relatively uniform quality regardless of UE locations in a
cell. Further, the multi-node system reduces signal loss generated
during transmission since base station(s) or base station
controller(s) connected to a plurality of nodes transmit/receive
data in cooperation with each other. When nodes spaced apart by
over a predetermined distance perform coordinated communication
with a UE, correlation and interference between antennas are
reduced. Therefore, a high signal to interference-plus-noise ratio
(SINR) can be obtained according to the multi-node coordinated
communication scheme.
[0009] Owing to the above-mentioned advantages of the multi-node
system, the multi-node system is used with or replaces the
conventional centralized antenna system to become a new foundation
of cellular communication in order to reduce base station cost and
backhaul network maintenance cost while extending service coverage
and improving channel capacity and SINR in next-generation mobile
communication systems.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide a method
for receiving and transmitting downlink control signal in the
wireless communication system.
[0011] It is to be understood that technical objects to be achieved
by the present invention are not limited to the aforementioned
technical objects and other technical objects which are not
mentioned herein will be apparent from the following description to
one of ordinary skill in the art to which the present invention
pertains.
[0012] The objects of the present invention can be achieved by
providing a method for receiving a downlink control signal by a
user equipment (UE) in a wireless communication system including:
receiving an Enhanced Physical Downlink Control Channel (EPDCCH)
from a downlink serving base station (BS); and monitoring a
plurality of EPDCCH candidates in an EPDCCH set contained in the
received EPDCCH, wherein a minimum aggregation level of the EPDCCH
candidates is associated with a downlink (DL) bandwidth of the
wireless communication system and downlink control information
(DCI) format.
[0013] Preferably, if the downlink (DL) bandwidth is comprised of
at least 25 resource blocks (RBs) and the DCI format is one of DCI
formats 2, 2A, 2B, 2C and 2D, the minimum aggregation level may be
2.
[0014] Preferably, if the number of PRB pairs constituting the
EPDCCH set is 4, 8, 4, 2, and 1 EPDCCH candidate(s) may be set to
aggregation levels 2, 4, 8, and 16, respectively.
[0015] Preferably, the method may further include: receiving
information regarding the number of EPDCCH candidates for each
aggregation level (L) from the downlink serving BS.
[0016] Preferably, if an aggregation level (hereinafter, "L1") is
set to be higher than the number of enhanced control channel
elements (ECCEs) contained in the EPDCCH set, the method may
further includes allocating EPDCCH candidates for the L1 to other
aggregation levels.
[0017] Preferably, the EPDCCH candidates for the L1 may be attempt
to be allocated to the other aggregation level with priority from
the highest aggregation level to the lowest aggregation level from
among aggregation levels less than the L1, from among aggregation
levels set in the EPDCCH set.
[0018] Preferably, if additional EPDCCH candidate cannot be
allocated to a specific aggregation level from among aggregation
levels less than the L1, the additional EPDCCH candidate may be
allocated to a next highest aggregation level subsequent to the
specific aggregation level.
[0019] Preferably, the number of EPDCCH candidate of the EPDDCH set
may be decided according to each aggregation level (L), the number
(N) of physical resource block (PRB) pairs of the EPDCCH set, and
the number of enhanced control channel elements (ECCEs) per PRB
pair, wherein the number of EPDCCH candidates for each N is
fixed.
[0020] Preferably, if two EPDCCH sets are present, the two EPDCCH
sets may be set to have different minimum aggregation levels.
[0021] Preferably, if two EPDCCH sets are present, the two EPDCCH
sets may be set in a manner that individual aggregation levels have
different numbers of EPDCCH candidates.
[0022] Preferably, if an aggregation level (hereinafter, "L2")
higher than the number of enhanced control channel elements (ECCEs)
contained in a first EPDCCH set is set in the first EPDCCH set,
EPDCCH candidate(s) for a specific aggregation level may be
allocated to a second EPDCCH set.
[0023] Preferably, the EPDCCH candidates for the L2 may be
attempted to be allocated to the second EPDCCH set with priority
from the highest aggregation level to the lowest aggregation level
from among aggregation levels less than the L2, from among
aggregation levels set in the first EPDCCH set.
[0024] Preferably, if additional EPDCCH candidate cannot be
allocated to a specific aggregation level from among aggregation
levels less than the L2, the additional EPDCCH candidates may be
allocated to a next highest aggregation level subsequent to the
specific aggregation level.
[0025] In accordance with another aspect of the present invention,
a user equipment (UE) configured to receive a downlink control
signal in a wireless communication system includes: a radio
frequency (RF) unit; and a processor configured to control the RF
unit, wherein the processor receives an Enhanced Physical Downlink
Control Channel (EPDCCH) from a downlink serving base station (BS),
and monitors a plurality of EPDCCH candidates in an EPDCCH set
contained in the received EPDCCH, wherein a minimum aggregation
level of the EPDCCH candidates is associated with a downlink (DL)
bandwidth of the wireless communication system and downlink control
information (DCI) format.
[0026] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
[0027] According to exemplary embodiments of the present invention,
the downlink control signal can be efficiently received and
transmitted in the wireless communication system.
[0028] It will be appreciated by persons skilled in the art that
the effects that can be achieved with the present invention are not
limited to what has been particularly described hereinabove and
other advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0030] FIG. 1 exemplarily shows a radio frame structure for use in
a wireless communication system.
[0031] FIG. 2 exemplarily shows a downlink/uplink (DL/UL) slot
structure for use in a wireless communication system.
[0032] FIG. 3 exemplarily shows a downlink (DL) subframe structure
for use in a 3GPP LTE/LTE-A system.
[0033] FIG. 4 exemplarily shows an uplink (UL) subframe for use in
a 3GPP LTE/LTE-A system.
[0034] FIG. 5 exemplarily shows EPDCCH(Enhanced Physical Downlink
Contorl Channel).
[0035] FIG. 6 exemplarily shows EPDCCH(Enhanced Physical Downlink
Contorl Channel).
[0036] FIG. 7 is a conceptual diagram illustrating a carrier
aggregation (CA) scheme.
[0037] FIG. 8 is a conceptual diagram illustrating a cross-carrier
scheduling scheme.
[0038] FIG. 9 is a conceptual diagram illustrating a method for
deciding the number of PRB pairs contained in an EPDCCH set
according to one embodiment of the present invention.
[0039] FIG. 10 is a conceptual diagram illustrating a method for
deciding PRB pairs contained in an EPDCCH set according to one
embodiment of the present invention,
[0040] FIG. 11 is a conceptual diagram illustrating an example for
indicating PRB pairs contained in an EPDCCH set according to one
embodiment of the present invention.
[0041] FIG. 12 is a block diagram of an apparatus for implementing
embodiment(s) of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0042] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. The accompanying drawings
illustrate exemplary embodiments of the present invention and
provide a more detailed description of the present invention.
However, the scope of the present invention should not be limited
thereto.
[0043] In some cases, to prevent the concept of the present
invention from being ambiguous, structures and apparatuses of the
known art will be omitted, or will be shown in the form of a block
diagram based on main functions of each structure and apparatus.
Also, wherever possible, the same reference numbers will be used
throughout the drawings and the specification to refer to the same
or like parts.
[0044] In the present invention, a user equipment (UE) is fixed or
mobile. The UE is a device that transmits and receives user data
and/or control information by communicating with a base station
(BS). The term `UE` may be replaced with `terminal equipment`,
`Mobile Station (MS)`, `Mobile Terminal (MT)`, `User Terminal
(UT)`, `Subscriber Station (SS)`, `wireless device`, `Personal
Digital Assistant (PDA)`, `wireless modem`, `handheld device`, etc.
A BS is typically a fixed station that communicates with a UE
and/or another BS. The BS exchanges data and control information
with a UE and another BS. The term `BS` may be replaced with
`Advanced Base Station (ABS)`, `Node B`, `evolved-Node B (eNB)`,
`Base Transceiver System (BTS)`, `Access Point (AP)`, `Processing
Server (PS)`, etc. In the following description, BS is commonly
called eNB.
[0045] In the present invention, a node refers to a fixed point
capable of transmitting/receiving a radio signal to/from a UE by
communication with the UE. Various eNBs can be used as nodes. For
example, a node can be a BS, NB, eNB, pico-cell eNB (PeNB), home
eNB (HeNB), relay, repeater, etc. Furthermore, a node may not be an
eNB. For example, a node can be a radio remote head (RRH) or a
radio remote unit (RRU). The RRH and RRU have power levels lower
than that of the eNB. Since the RRH or RRU (referred to as RRH/RRU
hereinafter) is connected to an eNB through a dedicated line such
as an optical cable in general, cooperative communication according
to RRH/RRU and eNB can be smoothly performed compared to
cooperative communication according to eNBs connected through a
wireless link. At least one antenna is installed per node. An
antenna may refer to an antenna port, a virtual antenna or an
antenna group. A node may also be called a point. Unlink a
conventional centralized antenna system (CAS) (i.e. single node
system) in which antennas are concentrated in an eNB and controlled
an eNB controller, plural nodes are spaced apart at a predetermined
distance or longer in a multi-node system. The plural nodes can be
managed by one or more eNBs or eNB controllers that control
operations of the nodes or schedule data to be transmitted/received
through the nodes. Each node may be connected to an eNB or eNB
controller managing the corresponding node via a cable or a
dedicated line. In the multi-node system, the same cell identity
(ID) or different cell IDs may be used for signal
transmission/reception through plural nodes. When plural nodes have
the same cell ID, each of the plural nodes operates as an antenna
group of a cell. If nodes have different cell IDs in the multi-node
system, the multi-node system can be regarded as a multi-cell (e.g.
macro-cell/femto-cell/pico-cell) system. When multiple cells
respectively configured by plural nodes are overlaid according to
coverage, a network configured by multiple cells is called a
multi-tier network. The cell ID of the RRH/RRU may be identical to
or different from the cell ID of an eNB. When the RRH/RRU and eNB
use different cell IDs, both the RRH/RRU and eNB operate as
independent eNBs.
[0046] In a multi-node system according to the present invention,
which will be described below, one or more eNBs or eNB controllers
connected to plural nodes can control the plural nodes such that
signals are simultaneously transmitted to or received from a UE
through some or all nodes. While there is a difference between
multi-node systems according to the nature of each node and
implementation form of each node, multi-node systems are
discriminated from single node systems (e.g. CAS, conventional MIMO
systems, conventional relay systems, conventional repeater systems,
etc.) since a plurality of nodes provides communication services to
a UE in a predetermined time-frequency resource. Accordingly,
embodiments of the present invention with respect to a method of
performing coordinated data transmission using some or all nodes
can be applied to various types of multi-node systems. For example,
a node refers to an antenna group spaced apart from another node by
a predetermined distance or more, in general. However, embodiments
of the present invention, which will be described below, can even
be applied to a case in which a node refers to an arbitrary antenna
group irrespective of node interval. In the case of an eNB
including an X-pole (cross polarized) antenna, for example, the
embodiments of the preset invention are applicable on the
assumption that the eNB controls a node composed of an H-pole
antenna and a V-pole antenna.
[0047] A communication scheme through which signals are
transmitted/received via plural transmit (Tx)/receive (Rx) nodes,
signals are transmitted/received via at least one node selected
from plural Tx/Rx nodes, or a node transmitting a downlink signal
is discriminated from a node transmitting an uplink signal is
called multi-eNB MIMO or CoMP (Coordinated Multi-Point Tx/Rx).
Coordinated transmission schemes from among CoMP communication
schemes can be categorized into JP (Joint Processing) and
scheduling coordination. The former may be divided into JT (Joint
Transmission)/JR (Joint Reception) and DPS (Dynamic Point
Selection) and the latter may be divided into CS (Coordinated
Scheduling) and CB (Coordinated Beamforming). DPS may be called DCS
(Dynamic Cell Selection). When JP is performed, more various
communication environments can be generated, compared to other CoMP
schemes. JT refers to a communication scheme by which plural nodes
transmit the same stream to a UE and JR refers to a communication
scheme by which plural nodes receive the same stream from the UE.
The UE/eNB combine signals received from the plural nodes to
restore the stream. In the case of JT/JR, signal transmission
reliability can be improved according to transmit diversity since
the same stream is transmitted from/to plural nodes. DPS refers to
a communication scheme by which a signal is transmitted/received
through a node selected from plural nodes according to a specific
rule. In the case of DPS, signal transmission reliability can be
improved because a node having a good channel state between the
node and a UE is selected as a communication node.
[0048] In the present invention, a cell refers to a specific
geographical area in which one or more nodes provide communication
services. Accordingly, communication with a specific cell may mean
communication with an eNB or a node providing communication
services to the specific cell. A downlink/uplink signal of a
specific cell refers to a downlink/uplink signal from/to an eNB or
a node providing communication services to the specific cell. A
cell providing uplink/downlink communication services to a UE is
called a serving cell. Furthermore, channel status/quality of a
specific cell refers to channel status/quality of a channel or a
communication link generated between an eNB or a node providing
communication services to the specific cell and a UE. In 3GPP LTE-A
systems, a UE can measure downlink channel state from a specific
node using one or more CSI-RSs (Channel State Information Reference
Signals) transmitted through antenna port(s) of the specific node
on a CSI-RS resource allocated to the specific node. In general,
neighboring nodes transmit CSI-RS resources on orthogonal CSI-RS
resources. When CSI-RS resources are orthogonal, this means that
the CSI-RS resources have different subframe configurations and/or
CSI-RS sequences which specify subframes to which CSI-RSs are
allocated according to CSI-RS resource configurations, subframe
offsets and transmission periods, etc. which specify symbols and
subcarriers carrying the CSI RSs.
[0049] In the present invention, PDCCH (Physical Downlink Control
Channel)/PCFICH (Physical Control Format Indicator Channel)/PHICH
(Physical Hybrid automatic repeat request Indicator Channel)/PDSCH
(Physical Downlink Shared Channel) refer to a set of time-frequency
resources or resource elements respectively carrying DCI (Downlink
Control Information)/CFI (Control Format Indicator)/downlink
ACK/NACK (Acknowledgement/Negative ACK)/downlink data. In addition,
PUCCH (Physical Uplink Control Channel)/PUSCH (Physical Uplink
Shared Channel)/PRACH (Physical Random Access Channel) refer to
sets of time-frequency resources or resource elements respectively
carrying UCI (Uplink Control Information)/uplink data/random access
signals. In the present invention, a time-frequency resource or a
resource element (RE), which is allocated to or belongs to
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH, is referred to as a
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE or
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH resource. In the
following description, transmission of PUCCH/PUSCH/PRACH by a UE is
equivalent to transmission of uplink control information/uplink
data/random access signal through or on PUCCH/PUSCH/PRACH.
Furthermore, transmission of PDCCH/PCFICH/PHICH/PDSCH by an eNB is
equivalent to transmission of downlink data/control information
through or on PDCCH/PCFICH/PHICH/PDSCH.
[0050] FIG. 1 illustrates an exemplary radio frame structure used
in a wireless communication system. FIG. 1(a) illustrates a frame
structure for frequency division duplex (FDD) used in 3GPP
LTE/LTE-A and FIG. 1(b) illustrates a frame structure for time
division duplex (TDD) used in 3GPP LTE/LTE-A.
[0051] Referring to FIG. 1, a radio frame used in 3GPP LTE/LTE-A
has a length of 10 ms (307200 Ts) and includes 10 subframes in
equal size. The 10 subframes in the radio frame may be numbered.
Here, Ts denotes sampling time and is represented as Ts=1/(2048*15
kHz). Each subframe has a length of ims and includes two slots. 20
slots in the radio frame can be sequentially numbered from 0 to 19.
Each slot has a length of 0.5 ms. A time for transmitting a
subframe is defined as a transmission time interval (TTI). Time
resources can be discriminated by a radio frame number (or radio
frame index), subframe number (or subframe index) and a slot number
(or slot index).
[0052] The radio frame can be configured differently according to
duplex mode. Downlink transmission is discriminated from uplink
transmission by frequency in FDD mode, and thus the radio frame
includes only one of a downlink subframe and an uplink subframe in
a specific frequency band. In TDD mode, downlink transmission is
discriminated from uplink transmission by time, and thus the radio
frame includes both a downlink subframe and an uplink subframe in a
specific frequency band.
[0053] Table 1 shows DL-UL configurations of subframes in a radio
frame in the TDD mode.
TABLE-US-00001 TABLE 1 Downlink- DL-UL to-Uplink config-
Switch-point Subframe number uration periodicity 0 1 2 3 4 5 6 7 8
9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S
U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D
D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D
[0054] In Table 1, D denotes a downlink subframe, U denotes an
uplink subframe and S denotes a special subframe. The special
subframe includes three fields of DwPTS (Downlink Pilot TimeSlot),
GP (Guard Period), and UpPTS (Uplink Pilot TimeSlot). DwPTS is a
period reserved for downlink transmission and UpPTS is a period
reserved for uplink transmission. Table 2 shows special subframe
configuration.
TABLE-US-00002 TABLE 2 Normal cyclic prefix in downlink UpPTS
Extended cyclic prefix in downlink Normal UpPTS cyclic Extended
Normal Special prefix cyclic cyclic Extended subframe in prefix
prefix in cyclic prefix configuration DwPTS uplink in uplink DwPTS
uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 7680
T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 20480 T.sub.s 2
21952 T.sub.s 23040 T.sub.s 3 24144 T.sub.s 25600 T.sub.s 4 26336
T.sub.s 7680 T.sub.s 4384 T.sub.s 5120 T.sub.s 5 6592 T.sub.s 4384
T.sub.s 5120 T.sub.s 20480 T.sub.s 6 19760 T.sub.s 23040 T.sub.s 7
21952 T.sub.s 12800 T.sub.s 8 24144 T.sub.s -- -- -- 9 13168
T.sub.s -- -- --
[0055] FIG. 2 illustrates an exemplary downlink/uplink slot
structure in a wireless communication system. Particularly, FIG. 2
illustrates a resource grid structure in 3GPP LTE/LTE-A. A resource
grid is present per antenna port.
[0056] Referring to FIG. 2, a slot includes a plurality of OFDM
(Orthogonal Frequency Division Multiplexing) symbols in the time
domain and a plurality of resource blocks (RBs) in the frequency
domain. An OFDM symbol may refer to a symbol period. A signal
transmitted in each slot may be represented by a resource grid
composed of N.sub.RB.sup.DL/UL*N.sub.sc.sup.RB subcarriers and
N.sub.symb.sup.DL/UL OFDM symbols. Here, N.sub.RB.sup.DL denotes
the number of RBs in a downlink slot and N.sub.RB.sup.UL denotes
the number of RBs in an uplink slot. N.sub.RB.sup.DL and
N.sub.RB.sup.UL respectively depend on a DL transmission bandwidth
and a UL transmission bandwidth. N.sub.symb.sup.DL denotes the
number of OFDM symbols in the downlink slot and N.sub.symb.sup.UL
denotes the number of OFDM symbols in the uplink slot. In addition,
N.sub.sc.sup.RB denotes the number of subcarriers constructing one
RB.
[0057] An OFDM symbol may be called an SC-FDM (Single Carrier
Frequency Division Multiplexing) symbol according to multiple
access scheme. The number of OFDM symbols included in a slot may
depend on a channel bandwidth and the length of a cyclic prefix
(CP). For example, a slot includes 7 OFDM symbols in the case of
normal CP and 6 OFDM symbols in the case of extended CP. While FIG.
2 illustrates a subframe in which a slot includes 7 OFDM symbols
for convenience, embodiments of the present invention can be
equally applied to subframes having different numbers of OFDM
symbols. Referring to FIG. 2, each OFDM symbol includes
N.sub.RB.sup.DL/UL*N.sub.sc.sup.RB subcarriers in the frequency
domain. Subcarrier types can be classified into a data subcarrier
for data transmission, a reference signal subcarrier for reference
signal transmission, and null subcarriers for a guard band and a
direct current (DC) component. The null subcarrier for a DC
component is a subcarrier remaining unused and is mapped to a
carrier frequency (f0) during OFDM signal generation or frequency
up-conversion. The carrier frequency is also called a center
frequency.
[0058] An RB is defined by N.sub.symb.sup.DL/UL (e.g. 7)
consecutive OFDM symbols in the time domain and R.sub.sc.sup.RB
(e.g. 12) consecutive subcarriers in the frequency domain. For
reference, a resource composed by an OFDM symbol and a subcarrier
is called a resource element (RE) or a tone. Accordingly, an RB is
composed of N.sub.symb.sup.DL/UL*N.sub.sc.sup.RB REs. Each RE in a
resource grid can be uniquely defined by an index pair (k, 1) in a
slot. Here, k is an index in the range of 0 to
N.sub.symb.sup.DL/UL*N.sub.sc.sup.RB-1 in the frequency domain and
1 is an index in the range of 0 to N.sub.symb.sup.DL/UL-1.
[0059] Two RBs, which occupy N.sub.sc.sup.RB same continuous
subcarriers for one subframe and are respectively located at two
slots of the subframe, will be referred to as a pair of physical
resource blocks (PRB). The two RBs constituting the PRB have the
same PRB number (or PRB index). A virtual resource block (VRB) is a
logical resource allocation unit for resource allocation. The VRB
has the same size as that of the PRB. The VRB may be divided into a
localized VRB and a distributed VRB depending on a mapping scheme
of VRB into PRB. The localized VRBs are mapped into the PRBs,
whereby VRB number (VRB index) corresponds to PRB number. That is,
nPRB=nVRB is obtained. Numbers are given to the localized VRBs from
0 to NDLVRB-1, and NDLVRB=NDLRB is obtained. Accordingly, according
to the localized mapping scheme, the VRBs having the same VRB
number are mapped into the PRBs having the same PRB number at the
first slot and the second slot. On the other hand, the distributed
VRBs are mapped into the PRBs through interleaving. Accordingly,
the VRBs having the same VRB number may be mapped into the PRBs
having different PRB numbers at the first slot and the second slot.
Two PRBs, which are respectively located at two slots of the
subframe and have the same VRB number, will be referred to as a
pair of VRBs.
[0060] FIG. 3 illustrates a downlink (DL) subframe structure used
in 3GPP LTE/LTE-A.
[0061] Referring to FIG. 3, a DL subframe is divided into a control
region and a data region. A maximum of three (four) OFDM symbols
located in a front portion of a first slot within a subframe
correspond to the control region to which a control channel is
allocated. A resource region available for PDCCH transmission in
the DL subframe is referred to as a PDCCH region hereinafter. The
remaining OFDM symbols correspond to the data region to which a
physical downlink shared chancel (PDSCH) is allocated. A resource
region available for PDSCH transmission in the DL subframe is
referred to as a PDSCH region hereinafter. Examples of downlink
control channels used in 3GPP LTE include a physical control format
indicator channel (PCFICH), a physical downlink control channel
(PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. The
PCFICH is transmitted at a first OFDM symbol of a subframe and
carries information regarding the number of OFDM symbols used for
transmission of control channels within the subframe. The PHICH is
a response of uplink transmission and carries an HARQ
acknowledgment (ACK)/negative acknowledgment (NACK) signal.
[0062] Control information carried on the PDCCH is called downlink
control information (DCI). The DCI contains resource allocation
information and control information for a UE or a UE group. For
example, the DCI includes a transport format and resource
allocation information of a downlink shared channel (DL-SCH), a
transport format and resource allocation information of an uplink
shared channel (UL-SCH), paging information of a paging channel
(PCH), system information on the DL-SCH, information about resource
allocation of an upper layer control message such as a random
access response transmitted on the PDSCH, a transmit control
command set with respect to individual UEs in a UE group, a
transmit power control command, information on activation of a
voice over IP (VoIP), downlink assignment index (DAI), etc. The
transport format and resource allocation information of the DL-SCH
are also called DL scheduling information or a DL grant and the
transport format and resource allocation information of the UL-SCH
are also called UL scheduling information or a UL grant. The size
and purpose of DCI carried on a PDCCH depend on DCI format and the
size thereof may be varied according to coding rate. Various
formats, for example, formats 0 and 4 for uplink and formats 1, 1A,
1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3A for downlink, have been defined
in 3GPP LTE. Control information such as a hopping flag,
information on RB allocation, modulation coding scheme (MCS),
redundancy version (RV), new data indicator (NDI), information on
transmit power control (TPC), cyclic shift demodulation reference
signal (DMRS), UL index, channel quality information (CQI) request,
DL assignment index, HARQ process number, transmitted precoding
matrix indicator (TPMI), precoding matrix indicator (PMI), etc. is
selected and combined based on DCI format and transmitted to a UE
as DCI.
[0063] In general, a DCI format for a UE depends on transmission
mode (TM) set for the UE. In other words, only a DCI format
corresponding to a specific TM can be used for a UE configured in
the specific TM.
[0064] A PDCCH is transmitted on an aggregation of one or several
consecutive control channel elements (CCEs). The CCE is a logical
allocation unit used to provide the PDCCH with a coding rate based
on a state of a radio channel. The CCE corresponds to a plurality
of resource element groups (REGs). For example, a CCE corresponds
to 9 REGs and an REG corresponds to 4 REs. 3GPP LTE defines a CCE
set in which a PDCCH can be located for each UE. A CCE set from
which a UE can detect a PDCCH thereof is called a PDCCH search
space, simply, search space. An individual resource through which
the PDCCH can be transmitted within the search space is called a
PDCCH candidate. A set of PDCCH candidates to be monitored by the
UE is defined as the search space. In 3GPP LTE/LTE-A, search spaces
for DCI formats may have different sizes and include a dedicated
search space and a common search space. The dedicated search space
is a UE-specific search space and is configured for each UE. The
common search space is configured for a plurality of UEs. The
aggregation levels defining the search space are indicated as
follows:
TABLE-US-00003 TABLE 3 Search Space Aggregation Size Number of
PDCCH Type Level L [in CCEs] candidates M.sup.(L) UE-specific 1 6 6
2 12 6 4 8 2 8 16 2 Common 4 16 4 8 16 2
[0065] A PDCCH candidate corresponds to 1, 2, 4 or 8 CCEs according
to CCE aggregation level. An eNB transmits a PDCCH (DCI) on an
arbitrary PDCCH candidate with in a search space and a UE monitors
the search space to detect the PDCCH (DCI). Here, monitoring refers
to attempting to decode each PDCCH in the corresponding search
space according to all monitored DCI formats. The UE can detect the
PDCCH thereof by monitoring plural PDCCHs. Since the UE does not
know the position in which the PDCCH thereof is transmitted, the UE
attempts to decode all PDCCHs of the corresponding DCI format for
each subframe until a PDCCH having the ID thereof is detected. This
process is called blind detection (or blind decoding (BD)).
[0066] The eNB can transmit data for a UE or a UE group through the
data region. Data transmitted through the data region may be called
user data. For transmission of the user data, a physical downlink
shared channel (PDSCH) may be allocated to the data region. A
paging channel (PCH) and downlink-shared channel (DL-SCH) are
transmitted through the PDSCH. The UE can read data transmitted
through the PDSCH by decoding control information transmitted
through a PDCCH. Information representing a UE or a UE group to
which data on the PDSCH is transmitted, how the UE or UE group
receives and decodes the PDSCH data, etc. is included in the PDCCH
and transmitted. For example, if a specific PDCCH is CRC (cyclic
redundancy check)-masked having radio network temporary identify
(RNTI) of "A" and information about data transmitted using a radio
resource (e.g. frequency position) of "B" and transmission format
information (e.g. transport block size, modulation scheme, coding
information, etc.) of "C" is transmitted through a specific DL
subframe, the UE monitors PDCCHs using RNTI information and a UE
having the RNTI of "A" detects a PDCCH and receives a PDSCH
indicated by "B" and "C" using information about the PDCCH.
[0067] A reference signal (RS) to be compared with a data signal is
necessary for the UE to demodulate a signal received from the eNB.
A reference signal refers to a predetermined signal having a
specific waveform, which is transmitted from the eNB to the UE or
from the UE to the eNB and known to both the eNB and UE. The
reference signal is also called a pilot. Reference signals are
categorized into a cell-specific RS shared by all UEs in a cell and
a modulation RS (DM RS) dedicated for a specific UE. A DM RS
transmitted by the eNB for demodulation of downlink data for a
specific UE is called a UE-specific RS. Both or one of DM RS and
CRS may be transmitted on downlink. When only the DM RS is
transmitted without CRS, an RS for channel measurement needs to be
additionally provided because the DM RS transmitted using the same
precoder as used for data can be used for demodulation only. For
example, in 3GPP LTE(-A), CSI-RS corresponding to an additional RS
for measurement is transmitted to the UE such that the UE can
measure channel state information. CSI-RS is transmitted in each
transmission period corresponding to a plurality of subframes based
on the fact that channel state variation with time is not large,
unlike CRS transmitted per subframe.
[0068] FIG. 4 illustrates an exemplary uplink subframe structure
used in 3GPP LTE/LTE-A.
[0069] Referring to FIG. 4, a UL subframe can be divided into a
control region and a data region in the frequency domain. One or
more PUCCHs (physical uplink control channels) can be allocated to
the control region to carry uplink control information (UCI). One
or more PUSCHs (Physical uplink shared channels) may be allocated
to the data region of the UL subframe to carry user data.
[0070] In the UL subframe, subcarriers spaced apart from a DC
subcarrier are used as the control region. In other words,
subcarriers corresponding to both ends of a UL transmission
bandwidth are assigned to UCI transmission. The DC subcarrier is a
component remaining unused for signal transmission and is mapped to
the carrier frequency f0 during frequency up-conversion. A PUCCH
for a UE is allocated to an RB pair belonging to resources
operating at a carrier frequency and RBs belonging to the RB pair
occupy different subcarriers in two slots. Assignment of the PUCCH
in this manner is represented as frequency hopping of an RB pair
allocated to the PUCCH at a slot boundary. When frequency hopping
is not applied, the RB pair occupies the same subcarrier.
[0071] The PUCCH can be used to transmit the following control
information. [0072] Scheduling Request (SR): This is information
used to request a UL-SCH resource and is transmitted using On-Off
Keying (OOK) scheme. [0073] HARQ ACK/NACK: This is a response
signal to a downlink data packet on a PDSCH and indicates whether
the downlink data packet has been successfully received. A 1-bit
ACK/NACK signal is transmitted as a response to a single downlink
codeword and a 2-bit ACK/NACK signal is transmitted as a response
to two downlink codewords. HARQ-ACK responses include positive ACK
(ACK), negative ACK (HACK), discontinuous transmission (DTX) and
NACK/DTX. Here, the term HARQ-ACK is used interchangeably with the
term HARQ ACK/NACK and ACK/NACK. [0074] Channel State Indicator
(CSI): This is feedback information about a downlink channel.
Feedback information regarding MIMO includes a rank indicator (RI)
and a precoding matrix indicator (PMI).
[0075] The quantity of control information (UCI) that a UE can
transmit through a subframe depends on the number of SC-FDMA
symbols available for control information transmission. The SC-FDMA
symbols available for control information transmission correspond
to SC-FDMA symbols other than SC-FDMA symbols of the subframe,
which are used for reference signal transmission. In the case of a
subframe in which a sounding reference signal (SRS) is configured,
the last SC-FDMA symbol of the subframe is excluded from the
SC-FDMA symbols available for control information transmission. A
reference signal is used to detect coherence of the PUCCH. The
PUCCH supports various formats according to information transmitted
thereon. Table 4 shows the mapping relationship between PUCCH
formats and UCI in LTE/LTE-A.
TABLE-US-00004 TABLE 4 Number of bits per PUCCH Modulation
subframe, format scheme M.sub.bit Usage Etc. 1 N/A N/A SR
(Scheduling Request) 1a BPSK 1 ACK/NACK or One SR + ACK/NACK
codeword 1b QPSK 2 ACK/NACK or Two SR + ACK/NACK codeword 2 QPSK 20
CQI/PMI/RI Joint coding ACK/NACK (extended CP) 2a QPSK + BPSK 21
CQI/PMI/RI + Normal CP ACK/NACK only 2b QPSK + QPSK 22 CQI/PMI/RI +
Normal CP ACK/NACK only 3 QPSK 48 ACK/NACK or SR + ACK/NACK or
CQI/PMI/RI + ACK/NACK
[0076] Referring to Table 4, PUCCH formats 1/1a/1b are used to
transmit ACK/NACK information, PUCCH format 2/2a/2b are used to
carry CSI such as CQI/PMI/RI and PUCCH format 3 is used to transmit
ACK/NACK information.
[0077] Reference Signal (RS)
[0078] When a packet is transmitted in a wireless communication
system, signal distortion may occur during transmission since the
packet is transmitted through a radio channel. To correctly receive
a distorted signal at a receiver, the distorted signal needs to be
corrected using channel information. To detect channel information,
a signal known to both a transmitter and the receiver is
transmitted and channel information is detected with a degree of
distortion of the signal when the signal is received through a
channel. This signal is called a pilot signal or a reference
signal.
[0079] When data is transmitted/received using multiple antennas,
the receiver can receive a correct signal only when the receiver is
aware of a channel state between each transmit antenna and each
receive antenna. Accordingly, a reference signal needs to be
provided per transmit antenna, more specifically, per antenna
port.
[0080] Reference signals can be classified into an uplink reference
signal and a downlink reference signal. In LTE, the uplink
reference signal includes:
[0081] i) a demodulation reference signal (DMRS) for channel
estimation for coherent demodulation of information transmitted
through a PUSCH and a PUCCH; and
[0082] ii) a sounding reference signal (SRS) used for an eNB to
measure uplink channel quality at a frequency of a different
network.
[0083] The downlink reference signal includes:
[0084] i) a cell-specific reference signal (CRS) shared by all UEs
in a cell;
[0085] ii) a UE-specific reference signal for a specific UE
only;
[0086] iii) a DMRS transmitted for coherent demodulation when a
PDSCH is transmitted;
[0087] iv) a channel state information reference signal (CSI-RS)
for delivering channel state information (CSI) when a downlink DMRS
is transmitted;
[0088] v) a multimedia broadcast single frequency network (MBSFN)
reference signal transmitted for coherent demodulation of a signal
transmitted in MBSFN mode; and
[0089] vi) a positioning reference signal used to estimate
geographic position information of a UE.
[0090] Reference signals can be classified into a reference signal
for channel information acquisition and a reference signal for data
demodulation. The former needs to be transmitted in a wide band as
it is used for a UE to acquire channel information on downlink
transmission and received by a UE even if the UE does not receive
downlink data in a specific subframe. This reference signal is used
even in a handover situation. The latter is transmitted along with
a corresponding resource by an eNB when the eNB transmits a
downlink signal and is used for a UE to demodulate data through
channel measurement. This reference signal needs to be transmitted
in a region in which data is transmitted.
[0091] General EPDCCH (Enhanced PDCCH)
[0092] Owing to introduction of a multi-node system, although
various communication schemes becomes available in a manner that
channel quality improvement is achieved, introduction of a new
control channel is being requested to apply the above-mentioned
MIMO scheme and inter-cell coordinated communication scheme to the
multi-node environment. Due to the above necessity, introduction of
a new control channel is an Enhanced PDCCH (EPDCCH) is being
intensively discussed, and the new control channel can be allocated
to a data region (hereinafter referred to as a PDSCH region)
instead of the legacy control region (hereinafter referred to as a
PDCCH region). As a result, node control information can be
transmitted per UE through EPDCCH, such that the problem of
insufficiency of the legacy PDCCH region can also be solved. For
reference, EPDCCH is not applied to the legacy UE, and can be
received by the LTE-A UE only.
[0093] FIG. 5 is a conceptual diagram illustrating a carrier
aggregation (CA) scheme.
[0094] Referring to FIG. 5, EPDCCH may define and use some parts of
the PDSCH region configured to transmit data, and the UE has to
perform blind decoding for detecting the presence or absence of
EPDCCH. EPDCCH performs the same scheduling operation (i.e., PDSCH,
PUSCH control) as in the legacy PDCCH. If the number of UEs
connected to the same node as in RRH increases, many more EPDCCHs
are allocated to the PDSCH region, such that the number of blind
decoding times to be executed by the UE increases, resulting in
increased complexity.
[0095] Meanwhile, a method for multiplexing EPDCCH for a plurality
of UEs needs to be considered. In more detail, according to the
multiplexing scheme proposed by the present invention, on the
condition that a common resource region (i.e., a common PRB set) is
configured, EPDCCHs of multiple UEs can be cross-interleaved to the
frequency domain or the time domain.
[0096] FIG. 6 is a conceptual diagram illustrating a method for
multiplexing EPDCCH for a plurality of UEs.
[0097] Specifically, FIG. 6(a) shows an example in which a common
PRB set is configured on the basis of a PRB pair and cross
increasing is performed on the basis of the common PRB set. In
contrast, FIG. 6(b) shows another example in which a common PRB set
is configured on a basis of a PRB and cross interleaving is
performed on the basis of the common PRB set. The schemes of FIGS.
6(a) and 6(b) have advantages in which a diversity gain of the
time/frequency domains extending a plurality of RBs can be
obtained.
[0098] Carrier Aggregation (CA)
[0099] Carrier aggregation will hereinafter be described in detail.
FIG. 7 is a conceptual diagram illustrating carrier aggregation
(CA).
[0100] Carrier aggregation refers to a method for allowing a UE to
use a plurality of frequency blocks or (logical) cells, each of
which is composed of uplink resources (or CCs) and/or downlink
resources (or CCs), as one large logical band so as to provide a
wireless communication system with a wider frequency bandwidth. For
convenience of description and better understanding of the present
invention, carrier aggregation will hereinafter be referred to as a
component carrier (CC).
[0101] Referring to FIG. 7, the entire system bandwidth (System BW)
includes a bandwidth of 100 MHz as a logical bandwidth. The entire
system bandwidth (system BW) includes five component carriers (CCs)
and each CC has a maximum bandwidth of 20 MHz. The CC includes one
or more physically contiguous subcarriers. Although all CCs have
the same bandwidth in FIG. 7, this is only exemplary and the CCs
may have different bandwidths. Although the CCs are shown as being
contiguous in the frequency domain in FIG. 8, FIG. 8 merely shows
the logical concept and thus the CCs may be physically contiguous
or separated.
[0102] Different center frequencies may be used for the CCs or one
common center frequency may be used for physically contiguous CCs.
For example, in FIG. 7, if it is assumed that all CCs are
physically contiguous, a center frequency A may be used. If it is
assumed that CCs are not physically contiguous, a center frequency
A, a center frequency B and the like may be used for the respective
CCs.
[0103] In the present specification, the CC may correspond to a
system band of a legacy system. By defining the CC based on the
legacy system, it is possible to facilitate backward compatibility
and system design in a radio communication environment in which an
evolved UE and a legacy UE coexist. For example, if the LTE-A
system supports carrier aggregation, each CC may correspond to the
system band of the LTE system. In this case, the CC may have any
one bandwidth such as 1.25, 2.5, 5, 10 or 20 MHz.
[0104] In the case in which the entire system band is extended by
carrier aggregation, a frequency band used for communication with
each UE is defined in CC units. A UE A may use 100 MHz which is the
bandwidth of the entire system band and perform communication using
all five CCs. Each of UEs B1 to B5 may only use a bandwidth of 20
MHz and perform communication using one CC. Each of UEs C1 and C2
may use a bandwidth of 40 MHz and perform communication using two
CCs. The two CCs may be contiguous or non-contiguous. The UE C1
uses two non-contiguous CCs and the UE C2 uses two contiguous
CCs.
[0105] One downlink CC and one uplink CC may be used in the LTE
system and several CCs may be used in the LTE-A system. At this
time, a method of scheduling a data channel by a control channel
may be divided into a linked carrier scheduling method and a cross
carrier scheduling method.
[0106] More specifically, in the linked carrier scheduling method,
similarly to the LTE system using a single CC, a control channel
transmitted via a specific CC schedules only a data channel via the
specific CC.
[0107] In contrast, in the cross carrier scheduling method, a
control channel transmitted via a primary CC using a carrier
indicator field (CIF) schedules a data channel transmitted via the
primary CC or another CC.
[0108] FIG. 8 is a conceptual diagram of a cross carrier scheduling
scheme.
[0109] Specifically, as can be seen from FIG. 8, the number of
cells (or CCs) allocated to a relay node (RN) is set to 3, cross
carrier scheduling is carried out using a CIF as described above.
In this case, it is assumed that a downlink cell (or CC) #A is set
to a primary downlink CC (i.e., a primary cell PCell), and the
remaining CCs #B and #C are used as secondary cells (SCells).
[0110] The present invention relates to an EPDCCH structure, and
more particularly to a method for selecting the number of PRBs
allocated to EPDCCH and a method for signaling this selection
method.
[0111] EPDCCH is designed to improve capacity of a control channel,
and can be transmitted to the legacy PDSCH region on the basis of
DMRS so as to obtain a beamforming region. For EPDCH transmission,
the eNB (or network) may signal specific information regarding an
EPDCCH transmission region to each UE. More specifically, the eNB
may inform the UE of K EPDCCH sets. Each EPDCCH set is composed of
N PRB pairs, and different EPDCCH sets may have different N values.
In addition, each EPCCH set may be classified into a localized
EPDCCH transmission purpose and a distributed EPDCCH transmission
purpose, and each EPDCCH set may entirely or partially overlap with
another EDPCCH set.
[0112] Configuration of N
[0113] N indicating the number of PRB pairs constructing each
EPDCCH set may be affected by a bandwidth (BW) of a scheduling cell
(hereinafter referred to as PCell) of EPDCCH and a bandwidth (BW)
of a cell (hereinafter referred to as SCell) scheduled by EPDCCH.
In case of PCell, if a sufficient BW (e.g., a narrow-bandwidth
system) is not given, the amount of resources capable of being
allocated for EPDCCH is limited, so that a relatively small value
needs to be assigned to N. Therefore, the number of RBs capable of
being allocated for EPDCCH is limited according to a PCell BW. if
the PCell BW is associated with the upper limit of N allocated to
EPDCCH transmission, SCell BW is associated with the lowest limit
of N allocated to EPDCCH transmission. The higher the SCell BW, the
higher the EDPCCH DCI payload, such that a minimum number of RBs
needed for transmission of the corresponding DCI is also increased.
Therefore, considering the PCell BW and the SCell BW, N needs to be
assigned a higher value than a minimum number of RBs needed for
EPDCCH transmission according to the SCell BW, and the upper limit
of N for use in PCell is set to a maximum number of RBs capable of
being allocated to EPDCCH transmission.
[0114] Therefore, the N value can be properly selected on the basis
of a BW of a PCell in which EPDCCH is transmitted. In one example,
a specific threshold BW value (T1) is decided so that N is set to
N1 at BW of T1 or less. If the BW value is higher than T1, N may be
set to N2 (N1.ltoreq.N2). In this case, each of N1 and N2 may be
the set of N values capable of being configured, and a threshold
value may be classified into two or more steps. For example, N may
be decided as represented by the following equation.
[0115] If BW.ltoreq.T1, then N1 (for example, {2, 4})
[0116] Otherwise, N2 (for example, {4, 8})
[0117] That is, N may be set to 2 or 4 at a BW that is equal to or
less than T1 RBs, and N may be set to 4 or 8 at a BW higher than T1
RBs.
[0118] In another method, the N value can be properly selected on
the basis of a BW of SCell scheduled by EPDCCH. In one method, a
specific threshold BW value and a T2 value are decided, so that N
may be set to N3 at a BW less than T2 and N may be set to N4 at a
BW higher than T2 (N3.ltoreq.N4). In this case, each of N3 and N4
may be the set of N values capable of being configured, and a
threshold value may be configured according to two or more steps.
For example, N may be decided as represented by the following
equation.
[0119] If BW.ltoreq.T2, then N3 (for example, {2, 4})
[0120] Otherwise, N4 (for example, {4,8})
[0121] That is, N may be set to 2 or 4 at a BW that is equal to or
less than T2 RBs, and N may be set to 4 or 8 at a BW higher than T2
RBs.
[0122] A threshold value of PCell and a threshold value of SCell
may be simultaneously applied. In this case, a configurable N value
of PCell and a configurable N value of SCell may be different from
each other in certain BW combinations from among available BW
combinations of PCell and SCell. Therefore, a configuration value
of a cell having a smaller N value from among N values of PCell and
SCell may be used. In other words, the range of configurable N
value may be decided according to the SCell BW, and N may be
limited to the range of a maximum number of RBs capable of being
allocated to PCell.
[0123] For example, if a threshold value of PCell and a threshold
value of SCell are simultaneously applied to the above-mentioned
example, the configuration range of an available N is shown in FIG.
9. If PCell can support up to {2, 4} on the condition that SCell
supports {4, 8} (i.e., BW of scheduling cell.ltoreq.T1 and BW of
scheduled cell>T2), the available N configuration range may
satisfy values of PCell. Likewise, if SCell supports up to {2, 4}
on the condition that PCell supports {4, 8} (i.e., BW of scheduling
cell>T1 and BW of scheduled cell.ltoreq.T2), the available N
configuration range may satisfy values of SCell.
[0124] A detailed description of a method for signaling N to a UE
after completion of N decision is as follows.
[0125] A method for informing a UE of an index value of a
configurable N through RRC signaling will hereinafter be described
in detail. If two configurable N values are given as in the case of
using the threshold value T1, 1-bit flag can be more simply used.
For example, if `flag=0` and `BW<T1` are given, N is set to 2
(N=2). If `flag=0` and `BW>T1` are given, N is set to 4 (N=4).
If `flag=1` and `BW.ltoreq.T1` are given, N is set to 4 (N=4). If
`flag=1` and `BW>T1` are given, N is set to 8 (N=8).
[0126] In another method, a specific threshold value is configured,
the UE determines whether an objective value is higher than the
threshold value, such that it is possible to determine/select which
one of N values will be used. The threshold value may be configured
in the number of available REs/PRB pairs, etc.
[0127] The number of available REs/PRB pairs<X.sub.thresh
(=104)
[0128] If BW.ltoreq.T1, then N={4}
[0129] Otherwise, N={8}
[0130] The number of available REs/PRB pairs.gtoreq.X.sub.thresh
(=104)
[0131] If BW.ltoreq.T1, then N={2}
[0132] Otherwise, N={4}
[0133] For example, the above-mentioned method can be defined as
the above expressions, and a detailed description thereof is shown
in FIG. 10.
[0134] PRB Allocation for EPDCCH Set
[0135] As described above, each EPDCCH set may be composed of N PRB
pairs, and the UE may obtain configuration of N PRB pairs
constructing an EPDCCH set through RRC signaling. In this case,
specific information as to which PRB from among all PRB sets will
be used as EPDCCH may be applied to the UE using the following
scheme.
[0136] A method for using bitmap will hereinafter be described. For
example, assuming that the entire DL system bandwidth is composed
of N.sub.tot RBs, specific information as to whether each RB is
allocated to EPDCCH may be signaled using N.sub.tot bits. if the
n-th bit is enabled (i.e., if the n-th bit is denoted by "1"), this
means that the n0th RB is allocated to EPDCCH. Bits indicating
RB(s) are not always sequentially mapped, and may be mapped in a
RB-to-bit format according to a predetermined rule. Two or more RBs
are configured to form a first group, such that EPDCCH may be
allocated to the RB group and may be indicated by bitmap.
[0137] FIG. 11 shows an example in which the entire band is
composed of 15 RBs for convenience of description and better
understanding of the present invention. In FIG. 11, bitmap may be
configured in any form of (a)010000100001000, (b)111000111000111,
and (c)000001011010110. Assuming that 3 RBs are configured to form
one group as shown in the form (b), the bitmap may be configured as
shown in `(b)10101`.
[0138] In another method, a combination of a number of a start RB
and the number of contiguous RBs may be signaled.
[0139] In another method, indexes of the corresponding pattern are
signaled according to the predefined pattern, such that PRB
information allocated to EPDCCH can be transferred. For example,
assuming that N RBs are allocated to EPDCCH, floor (i.e., system
BW/N) patterns in which individual RBs are distributed at equal
intervals within the entire system band may be considered and used.
The eNB or BS may indicate the corresponding allocation using
ceiling(log 2(the number of patterns)) bits.
[0140] FIG. 11(a) shows the exemplary case of N.sub.tot=15 and N=3.
If the equal-spacing distribution pattern is defined for the entire
system band, a spacing between RBs constructing a specific pattern
is denoted by "15RB/3=5RB" and 5 patterns are present. If the
smallest RB index of each pattern is used as the pattern index,
FIG. 11(a) shows a specific pattern corresponding to `pattern
index=1` from among 5 patterns.
[0141] Through a combination of intervals that are not defined by
an arbitrary start PRB index and a system bandwidth/N, PRBs spaced
apart from the corresponding start PRB index by a predetermined
distance can be selected for EPDCCH. In this case, if indexes (or
locations) of PRB pairs constructing the corresponding EPDCCH set
exceed the range of a system BW, a cyclic shifting calculation
scheme of the corresponding PRB-pair index (or location) may be
used. In this case, the cyclic shifting calculation scheme may be
represented by "PRB pair index (or location) mod the number of PRB
pairs constructing the system BW".
[0142] Likewise, the pattern may also be constructed using a
combination of intervals that are not defined by the arbitrary
start PRB index and the system BW/N, and an arbitrary pattern may
be defined so that indexes may be allocated to each pattern.
[0143] Aggregation Level and Construction of the Number of
Corresponding Blind Decoding Times
[0144] On the other hand, if N (i.e., the number of PRB pairs)
allocated to EPDCCH has a low value in the same manner as in the
narrow band system, it may be difficult to construct a search space
in a high aggregation level (AL). For example, if N=2 is
configured, each PRB pair includes 4 ECCEs, it may be impossible to
configure the search space of AL=8 or higher. If each PRB pair
includes 2 ECCEs, it may be impossible to configure the search
space of AL=4 or higher. Therefore, the search space of the
corresponding AL may be allocated to another AL. That is, blind
decoding complexity (i.e., the number of blind decoding attempts)
of the EPDCCH set of the UE is constantly maintained, resulting in
performance improvement.
[0145] Therefore, the number of blind decoding times of each AL
(i.e., the number of PDCCH candidates) may be differently
configured according to each EPDCCH set allocated to the UE. For
example, if ALs higher than the number of ECCEs contained in the
EPDCCH set are configured, all the ePDCCH candidates for the
corresponding ALs may be allocated to the lowest AL or may be
maximally and evenly allocated to ALs lower than the corresponding
AL. For example, assuming that {6,6,2,2} is assigned to PDCCH or
ePDCCH candidate (hereinafter referred to as a candidate)
associated with AL={1,2,4,8}, if N=2 and the number of ECCEs per
PRB pair (i.e., # of ECCE/PRB pair) is set to 2, the number of
ECCEs per EPDCCH set (# of ECCE/EPDCCH set) is set to 4, BLD for
AL=8 is not performed. Therefore, two candidates capable of being
allocated to AL=8 are not initially allocated (0), may be allocated
to AL=1 corresponding to the lowest AL (0), or and may be
sequentially allocated in the range from the lowest AL to a maximum
allowable AL (0).
TABLE-US-00005 TABLE 5 Aggregation #of BD level Legacy 1 6 6 8 7 2
6 6 6 7 4 2 2 2 2 8 2 0 0 0
[0146] The number of candidates for each AL may be transferred to
the UE through RRC signaling or the like. That is, the eNB may
configure not only N but also the number of candidates of each Al
when configuring the EPDCCH set. For example, when one EPDCCH set
is configured, the number of BD attempt times may be set to (# of
BD)={6,6,2,2} in association with each of AL={1, 2, 4, 8}. In order
to reduce signaling overhead, the number of configurable
combinations of (# of BD) is preset to a finite number and may be
configured by the corresponding indexes only.
TABLE-US-00006 TABLE 6 index # of BD for each aggregation level 0
{6, 6, 2, 2} 1 {8, 4, 2, 2} 2 {4, 4, 4, 4} . . . . . .
[0147] It is obvious to those skilled in the art that the term "AL"
described in the above-mentioned embodiment is only exemplary and
may be set to another value through the predefined rule or
signaling. Likewise, the number of BD attempt times interworking
with (or allocated to) a specific AL may be assigned a different
value (through the predefined rule or signaling). For example, in
association with this different value, the number of BD attempts
associated with each of AL={1, 2, 4, 8} may be respectively
configured as {6,6,2,2}.
[0148] In this case, exception processing of the case in which the
number (# of ECCE within a configured EPDCCH set) of ECCEs
contained in the configured EPDCCH set is less than a specific AL
may be directly or indirectly carried out. In case of using the
direct scheme, the eNB selects an appropriate scheme and
re-distributes the number of candidates so as to perform UE
reconfiguration, or the eNB may transfer an index corresponding to
a new combination to the UE.
[0149] In case of using the indirect scheme, if exception occurs,
the UE may perform exception processing according to a
predetermined rule. For example, assuming that an exception
processing matter between the eNB and the UE occurs and the scheme
{circle around (1)} is promised to be used, the UE does not perform
blind decoding (BD) for a non-supported AL, and satisfies initial
configuration of the remaining AL without change.
[0150] In case that the number (# of ECCE within a configured
EPDCCH set) of ECCEs in the configured EPDCCH set is less than a
specific AL, (# of ECCE within a configured EPDCCH set) may be
affected by the N value, the AL at which the number (# of ECCE/PRB
pair) of ECCEs per PRB pair should be changed or supported is
changed to another, the above-mentioned case may occur.
[0151] In accordance with one example in which the number (# of
ECCE within a configured EPDCCH set) of ECCEs contained in the
configured EPDCCH set is changed to another in association with the
same N, the number (# of ECCE/PRB pair) of ECCEs per PRB pair in a
specific-type subframe such as a special subframe may be reduced to
1/k of another subframe. In this case, if N is set to the same
value, the number "(# of ECCE within a configured EPDCCH set) (=#
of ECCE within N PRB pair)" of ECCEs contained in the configured
EPDCCH set may be reduced to 1/k. In another example, AL may be
changed to another and CSI-RS signals may be allocated to the
corresponding subframe, and the number (# of RE/PRB pair) of REs
per available PRB pair is reduced to 1/m. In this case, AL to be
supported is increased m times, and a detailed description thereof
is summarized as follows.
[0152] # of ECCE within N PRB pair.ltoreq. (or <) AL may occur
in the following cases 1), 2), and 3).
[0153] 1) N is reduced.fwdarw. N configuration may be achieved for
N increment
[0154] 2) # of ECCE/PRB pair reduction
[0155] 3) AL increment
[0156] The first case (1) and a method for allocating the number of
BD attempt times for use in the first case (1) have already been
disclosed. As one example of the second case (2), if "# of ECCE/PRB
pair=4" is decided at N=2, this means that AL may be assigned a
maximum value of 8 as denoted by AL=8. However, if "# of ECCE/PRB
pair" is changed to 2 (# of ECCE/PRB pair=2), AL may be assigned a
maximum value of 4 as denoted by AL=4. As one example of the third
case (3), when (# of RE/PRB pair) is reduced to 104 or less, there
may arise another case in which AL to be supported may be changed
from {1,2,4,8} to {2,4,8,16}. If the number of available REs per
PRB pair is less than 104, it may be difficult to transmit DCI
payload using only one ECCE. For example, a normal subframe having
a normal CP may be configured by 4 ECCEs per PRB pair. In this
case, if the number of available REs per PRB pair is less than 104,
26 or less REs may be contained in each ECCE, so that it may be
difficult to perform DCI loading. Accordingly, a minimum AL is
increase by one step, and many more ECCEs are contained in EPDCCH,
such that DCI can be transmitted. In this case, if N=2 and "# of
ECCE/PRB pair=4" are given, it may be impossible to configure
"AL=16".
[0157] Even in the second case 2) and the third case 3), if a
non-supported AL occurs in the same manner as in the first case 1),
the number (i.e., the number of EPDCCH candidates) of BD attempts
allocated to the corresponding AL may be allocated to another AL
using any one of the third methods ({circle around (1)}, {circle
around (2)}, and {circle around (3)}).
[0158] A different value may be assigned to AL as necessary. For
example, AL may be limited to 4 or less only in the case of
localized transmission (so that all candidates can be configured in
one PRB pair.) As described above, if only AL having a smaller
range than the preconfigured AL combination is supported, the
number of BD attempts for each AL may be derived and decided from
the number of BD attempts for the preconfigured AL combination
using any one of the above-mentioned methods ({circle around (1)},
{circle around (2)}, and {circle around (3)}).
[0159] BD Candidate Allocation for Plural EPDCCH Sets
[0160] On the other hand, the UE may be configured as at least two
EPDCCH sets. In this case, the BD candidate may be classified
according to each EPDCCH set, and the number of candidates
allocated to available Als of each EPDCCH set may be configured by
the network or may be decided by an implicit rule. However, a total
number of BD candidates needs to be maintained at a level similar
to the legacy level.
[0161] In order to allocate the number of BD candidates according
to the implicit rule, it is necessary to design a predetermined
rule applicable to the number of configurable EPDCCH sets, a
transmission (Tx) mode, and an available Al combination. For
example, a maximum of two EPDCCH sets may be configured, and AL may
consider an exemplary case in which each EPDCCH set can support {1,
2, 4, 8}. In this case, the number of BD candidates may be decided
as shown in he following Table 7.
TABLE-US-00007 TABLE 7 AL Set 1 Set 2 1(2) 3 3 2(4) 3 3 4(8) 1 1
8(16) 1 1
[0162] If a specific set cannot support all ALs, BD performance for
a non-supported AL may be independently distributed to another AL
for each set, or BD for the corresponding AL may not be
performed.
[0163] In another method, the number of BD candidates for each AL
may be constantly maintained within the entire set. If all ALs are
not supported in a specific set and the remaining sets support the
corresponding AL, the BD candidate for the non-supported AL can be
supported from the remaining sets. If the corresponding AL is not
supported even in other sets, reallocation of the BD candidate can
be achieved within the same set. In this case, another set may
include a legacy PDCCH. In case of (# of REs/PRB
pair<X.sub.thresh), if a supportable Al is changed to {2,4,8,16}
and the number (N1) of PRB pairs of the set 1 is set to 2, it is
impossible to construct "AL=16" in the corresponding set, and two
candidates can be allocated to "AL=16" of the set 2. If the number
(N2) of PRB pairs of the set 2 is not sufficient to support to the
two candidates (for example, N2=4), the corresponding BD candidate
may be allocated to AL=2 or the like.
TABLE-US-00008 TABLE 8 Set 1 (N1 = 2) Set 2 (N2 = 8) 2 3 3 4 3 3 8
1 1 16 0 2
TABLE-US-00009 TABLE 9 Set 1 (N1 = 2) Set 2 (N2 = 4) 2 3 4 4 3 3 8
1 1 16 0 1
[0164] On the other hand, a primary set having a predetermined
level of N is defined, and a secondary set having special
limitation to N may be defined within the configurable range. A
predetermined value is assigned to the level (N) of the primary
set, and a minimum N value capable of supporting a maximum AL can
be promised in the arbitrary configuration. For example, assuming
that "# of ECCEs/PRB pair=4" and "maximum AL=16" are given, or
assuming that "# of ECCEs/PRB pair=2" and "maximum AL=8" are given,
if a maximum value of N is given, a minimum N value of the primary
set may be set to 4. In this case, if it is impossible to assign a
predetermined number or higher to a maximum number of AL candidates
(the candidate mapped to the same ECCE occurs), it is necessary to
configure the N value in consideration of a maximum number of
candidates. For example, if N=4 is given, only one candidate for
AL=8 can be configured. Therefore, if two or more candidates of
AL=8 are allocated, N of the primary set may be assigned 8 or
higher.
[0165] Since the primary set guarantees a maximum AL, AL is
classified into a high AL "high" and a low AL "low", ALs contained
in "high" may be assigned to the primary set, and ALs contained in
"low" may be assigned to the secondary set. As an absolute method
for discriminating between "high" and "low", an arbitrary AL (e.g.,
AL=4) or higher may be configured in "high". Alternatively, the
above-mentioned method may also be decided in consideration of a
relative level of the configurable AL. For example, in case of
supporting "AL=1, 2, 4, 8", AL=1,2 may be identified by "low" and
AL=4,8 may be identified by "high". If (# of REs/PRB
pair<X.sub.thresh) is changed and AL is also changed to
{2,4,8,16}, AL=2,4 may be identified by "low" and AL=8,16 may be
identified by "high". In case of using the above-mentioned method,
the BD candidate is allocated as follows.
TABLE-US-00010 TABLE 10 AL Primary Set (N1 = 8) Secondary Set (N2 =
2) 1(2) 0 6 2(4) 0 6 4(8) 2 0 8(16) 2 0
[0166] In case of the secondary set, assuming that it is impossible
to configure a specific AL at the configured N value due to
insufficiency of available resources, the corresponding AL
candidate may be allocated only to the primary set. For example,
assuming that the secondary set is configured as N2=2 and (# of
REs/PRB.sub.pair<X.sub.thresh) is given, if AL is changed from
{1,2,4,8} to {2,4,8,16}, it is impossible to configure the
candidate having AL=16 within the secondary set. In this case, the
candidate corresponding to AL=16 may be entirely allocated to the
primary et.
TABLE-US-00011 TABLE 11 AL Primary Set (N1 = 8) Secondary Set (N2 =
2) 2 3 3 4 3 3 8 1 1 16 2 0
[0167] The above-mentioned concept can also be applied to the
exemplary case (See Table 10) in which AL is classified into a high
AL "high" and a low AL "low" so that only the low AL can be
allocated. Although only the low AL is assigned, an excessively low
value may be assigned to N, or the subframe type is changed, such
that a higher N value is needed for the same AL due to reduction of
"# of ECCE/PRB pair". (Likewise, due to reduction of (# of RE/PRB
pair), AL is increased so that a higher N value is needed for the
same DCI transmission).
[0168] The implicit rule is applied to the above-mentioned scheme.
Assuming that AL for each EPDCCH set and the number of BD
candidates corresponding to each AL are predefined, the
above-mentioned scheme may be used when arbitrary EPDCCH sets are
allocated. In another method, the network allocates the number of
BD candidates for each EPDCCH set and may inform the UE of the
allocated information. In this case, the network may allocate the
BD candidate to AL of each set using the same method.
[0169] If the network configures the number of BD candidates, an
arbitrary combination having full flexibility may be considered
under limitation (having a similar level as in the legacy art)
regarding a total number of BD candidates. In this case,
non-negligible overhead may occur. Accordingly, the number of BD
candidates may be calculated according to the implicit rule, and an
exceptional situation in which a specific AL cannot be configured
at the same N value due to change of the subframe type can be
decided according to the implicit rule.
[0170] Exceptional processing in which the number of ECCEs
contained in the configured EPDCCH set is less than AL has already
been disclosed in detail. That is, when the number of BD candidates
is allocated to each AL, the number of candidates capable of being
configured by a specific AL may be limited. As described above, if
it is impossible to construct as many candidates as a predetermined
number of BD candidates in the corresponding AL, the number of the
remaining BD candidates is allocated to another AL. In this case,
the number of remaining candidates may be re-allocated in a manner
that the remaining BD candidates can sequentially fill the
individual ALs starting from the highest AL from among ALs of the
corresponding AL or less. That is, the number of redundant BD
candidates obtained after the BD candidates are allocated to a
maximum AL from among ALs of the corresponding AL or less may be
primarily allocated to the next high AL, such that this BD
candidate allocation scheme can be repeated as described above. The
above-mentioned process may be performed to the range of the
smallest AL, or may be repeatedly performed to a predetermined
minimum AL. If the remaining BD candidates are present after
completion of allocation to a minimum AL within the corresponding
set, the corresponding BD candidate may not be allocated any more,
or may be transferred to another set.
[0171] As described above, the operation for giving priority of the
BD candidate allocation to a high AL may be used to guarantee
candidates for the case in which DCI is transmitted using the high
AL. That is, assuming the operation for constructing a relatively
high AL is limited by the number of ECCEs constructing EPDCCH, the
corresponding candidate is reallocated to the next order AL (i.e.,
the next high AL), such that it has fairness with the relatively
low AL. For example, if a high AL is needed in a poor channel
environment, the operation for allocating an additional candidate
to the low AL having a sufficient number of candidates may be
meaningless.
[0172] For example, if a reference (AL=L) is provided in a given
situation, it is assumed that {6, 6, 2, 2} BD candidates can be
allocated to AL=L, 2L, 4L, 8L, respectively, such that the
above-mentioned embodiment is based on the above assumption. In
this case, assuming that 8 PRB pairs are given, a total of 32 ECCEs
may be generated and a reference (L=4) is assumed, and it is also
assumed that AL=32 is not present due to consumption of the
excessive amount of resources. Two candidates for AL=32
corresponding to 8L may be allocated to another AL, and may attempt
to perform allocation to the highest AL (AL=16) from among ALs
lower than `AL=32`, and two candidates present in `AL=16` consume
all of 32 ECCEs, such that it is impossible to allocate the
additional candidate to AL=16. Therefore, allocation to AL-8
corresponding to the next AL is attempted, and 32 ECCEs can make a
total of four `AL-8` candidates, such that two candidates from
among 6 allocation candidates remain unused. Therefore, a total of
four redundant candidates may attempt to perform allocation to
AL=4. A total of 8 candidates may be present in case of AL-8, such
that two redundant candidates are allocated to AL=4 and the last
two redundant candidates are allocated to AL=2. As a result, {0, 2,
8, 4, 2} candidates are respectively allocated to AL=1, 2, 4, 8,
16.
[0173] The following Table 12 shows an exemplary case in which the
BS candidate is allocated in response to each situation. In this
case, if a reference level is set to 4, it is assumed that no
ePDCCH set is configured as two PRB pairs, and it is also assumed
that AL-1 is not present in case of "Reference L=4".
TABLE-US-00012 TABLE 12 Reference L = 1 Reference L = 2 Reference L
= 4 2 PRB pairs {8, 4, 2, 1, 0} {0, 4, 2, 1, 0} -- 4 PRB pairs {6,
6, 2, 2, 0} {0, 8, 4, 2, 1} {0, 8, 4, 2, 1} 8 PRB pairs {6, 6, 2,
2, 0} {0, 6, 6, 2, 2} {0, 2, 8, 4, 2}
[0174] In addition, the following table shows an exemplary case in
which the BD candidate is allocated to two EPDCCH sets on the basis
of a reference applied to the above-mentioned embodiment. In this
case, N1 denotes the number of PRB pairs of a first EPDCCH set 1,
and N2 denotes the number of PRB pairs of a second EPDCCH set 2. BW
denotes a system bandwidth, and Min AL indicates a minimum AL
capable of being transmitted in a given subframe. MinAL may be
changed in the case in which the number of available REs per PRB
pair is at a relatively low number as described above. For example,
if the number of available REs per PRB pair is less than 104, MinAL
may be changed to 2. The reference L for use in the following table
is assumed as follows.
[0175] Reference L=4 [0176] Case in which Min AL is 2 (MinAL=2) and
DCI format 2 series are used under the condition that BW is larger
than 25*RB
[0177] Reference L=2 [0178] Case in which Min AL is 2 (MinAL=2) and
DCI format 0/1 series are used under the condition that BW is
larger than 25*RB [0179] Case in which Min AL is 1 (MinAL=1) and
DCI format 2 series are used under the condition that BW is larger
than 25*RB [0180] Case in which Min AL is 2 (MinAL=2) and DCI
format 0/1 series are used under the condition that BW is larger
than 25*RB [0181] Case in which Min AL is 2 (MinAL=2) and DCI
format 2 series are used under the condition that BW is larger than
25*RB
[0182] Reference L=1
[0183] In the remaining cases other than the above cases:
[0184] In this case, it is assumed that the BD candidate is equally
allocated to each EPDCCH set. That is, generally, {3,3,1,1}
candidates are respectively allocated to AL=L, 2L, 4L, 8L.
TABLE-US-00013 TABLE 13 Min AL = 1 Min AL = 2 DCI format DCI format
DCI format DCI format BW N1 N2 0/1/1A/ . . . 2/2B/2C/2D . . .
0/1/1A/ . . . 2/2B/2C/2D . . . <=25 RB 2 0 {8, 4, 2, 1, 0}, {8,
4, 2, 1, 0}, {0, 4, 2, 1, 0}, {0, 4, 2, 1, 0}, {0, 0, 0, 0, 0} {0,
0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} <=25 RB 2 2 {3, 3,
1, 1, 0}, {3, 3, 1, 1, 0}, {0, 4, 2, 1, 0}, {0, 4, 2, 1, 0}, {3, 3,
1, 1, 0} {3, 3, 1, 1, 0} {0, 4, 2, 1, 0} {0, 4, 2, 1, 0} <=25 RB
4 0 {6, 6, 2, 2, 0}, {6, 6, 2, 2, 0}, {0, 8, 4, 2, 1}, {0, 8, 4, 2,
1}, {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0}
<=25 RB 4 2 {3, 3, 1, 1, 0}, {3, 3, 1, 1, 0}, {0, 3, 3, 1, 1},
{0, 3, 3, 1, 1}, {3, 3, 1, 1, 0} {3, 3, 1, 1, 0} {0, 4, 2, 1, 0}
{0, 4, 2, 1, 0} <=25 RB 4 4 {3, 3, 1, 1, 0}, {3, 3, 1, 1, 0},
{0, 3, 3, 1, 1}, {0, 3, 3, 1, 1}, {3, 3, 1, 1, 0} {3, 3, 1, 1, 0}
{0, 3, 3, 1, 1} {0, 3, 3, 1, 1} >25 RB 4 0 {6, 6, 2, 2, 0}, {0,
8, 4, 2, 1}, {0, 8, 4, 2, 1}, {0, 8, 4, 2, 1}, {0, 0, 0, 0, 0} {0,
0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} >25 RB 4 4 {3, 3, 1,
1, 0}, {0, 3, 3, 1, 1}, {0, 3, 3, 1, 1}, {0, 1, 4, 2, 1}, {3, 3, 1,
1, 0} {0, 3, 3, 1, 1} {0, 3, 3, 1, 1} {0, 1, 4, 2, 1}, >25 RB 8
0 {6, 6, 2, 2, 0}, {0, 6, 6, 2, 2}, {0, 6, 6, 2, 2}, {0, 2, 8, 4,
2}, {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0} {0, 0, 0, 0, 0}
>25 RB 8 4 {3, 3, 1, 1, 0}, {0, 3, 3, 1, 1}, {0, 3, 3, 1, 1},
{0, 0, 3, 3, 2}, {3, 3, 1, 1, 0} {0, 3, 3, 1, 1} {0, 3, 3, 1, 1}
{0, 1, 4, 2, 1}
[0185] The reference level L is not always limited to values used
in the above example, and is not always fixed to values used in the
above table. That is, L may also be set to any of the remaining
values other than 1, 2, and 4. EPDCCH localized or distribute
scheme and other EPDCCH properties are additionally considered so
that other L values may also be considered in the same condition as
in the above table.
[0186] On the other hand, when a certain configuration is achieved
through comparison between a specific threshold value and other
values according to the embodiments, it is obvious to those skilled
in the art that the term ("below" or "above") including a specific
threshold value, or the term ("less than" or "higher than")
including the specific threshold value may or may not include a
specific threshold value.
[0187] Meanwhile, the reference level L for each EPDCCH set may be
differently configured. For example, each EPDCCH set may be
transferred from different TPs according to the same scenario as in
DPS. In this case, If TP1 uses 2-port-CRS and TP2 uses 4-port-CRS,
the number of available REs of EPDCCH set 1 transmitted from TP1 in
a single PRB pair may be higher than X.sub.thresh, and the number
of available REs of EPDCCH set 2 transmitted from TP2 may be less
than X.sub.thresh. Accordingly, the reference level L for use in
EPDCCH set 1 may be assigned L1=1, and the reference level L for
use in EPDCCH set 2 may be assigned L2=2.
[0188] As described above, if different reference levels (L) are
assigned to individual EPDCCH sets, the following two schemes for
splitting the BD candidate to the individual sets may be used.
[0189] First Step: Assuming that individual EPDCCH sets have the
same reference level L and the BD candidate is split, splitting of
the BD candidate is performed.
[0190] That is, assuming that L1=1 of EPDCCH set 1 and L2=2 of
EPDCCH set 2 are given, it is assumed that L=1 is assigned to two
sets or the BD candidate can be split on the assumption of L=2. For
example, if N1=4 and L1=1 are assigned for the set 1, and if the
N2=8 and L2=2 are assigned for the set 2, BD allocation can be
achieved as follows. [0191] Set 1: If L=1 and N1=4 are given, (# of
BD candidate={3,3,1,1,0}) for AL={1,2,4,8,16} can be decided.
[0192] Set 2: If L=1 and N2=8 are given, (# of BD
candidate={3,3,1,1,0}) for AL={1,2,4,8,16} can decided.
[0193] Second Step: Different L values can be corrected. In the
first step, assuming that BD allocation is performed at L=L1 (i.e.,
if it is assumed that the reference level L is set to L1 in the
first step on the condition that L1 and L2 are different from each
other), it is necessary to coordinate AL of the BD candidate of
EPDCCH set (i.e., EPDCCH set 2) having L2. If it is impossible to
support all the BD candidates allocated to a maximum AL after
completion of coordination, a redundant BD candidate incapable of
supporting other ALs can be reallocated. The reallocation scheme
may use any one of the above-mentioned schemes. The following sets
1 and 2 can be obtained through coordination of BD allocation of
the set 2. [0194] Set 1: If L=1 and N1=4 are given, (# of BD
candidate={3,3,1,1,0}) for AL={1,2,4,8,16} can be decided. [0195]
Set 2: If L2=2 and N2=8 are given, (# of BD candidate=10,3,3,1,11)
for AL={1,2,4,8,16} can decided.
[0196] In this case, information as to which one of EPDCCH sets
will be used as the reference L of the first step and information
as to which one of EPDCCH sets will be corrected in the second step
are of little importance. That is, although the first step is
performed on the basis of EPDCCH Set 1 and L=1, and correction is
performed in the second step on the basis of EPDCCH Set 2 and L2=2
for convenience of description, the scope or spirit of the present
invention is not limited thereto.
[0197] For example, the above-mentioned operation may also be
carried out on the basis of the EPDCCH set transmitted by a serving
cell. Assuming that the EPDCCH set transmitted by the serving cell
is denoted by Set 1 and L1=2, and the EPDCCH set 2 transmitted from
other TPs is denoted by L2=1, the first step is performed at the
reference level (L=2) and BD allocation of the EPDCCH set 2 can be
coordinated in the second step. Alternatively, the above-mentioned
operation may also be performed on the basis of a minimum L from
among EPDCCH sets. In this case, the reference level (L2-1) of the
EPDCCH set 2 transmitted at TP2 is used as a reference of the first
step so as to assume L1=1. and BD allocation of the EPDCCH set 1
can be coordinated in the second step.
[0198] Meanwhile, if the BD candidate is allocated to two or more
EPDCCH sets, different numbers of BD candidates related to
individual sets may be allocated to individual sets. For example,
the number of candidates per set may be defined by a function for N
and L. For example, NIL is used as a reference of BD splitting so
as to reflect the number of available REs. In this case, if
different N values are assigned to the same L, different numbers of
BD may be assigned to individual sets. If different L values are
assigned to the same N, different numbers of BD may be assigned to
individual sets. In contrast, although different N and L values are
assigned to individual sets, if the same N/L values are given, the
same number of BD can be allocated to the individual sets.
[0199] Therefore, as one method for considering the N/L values
during BD splitting for each set, the number of BD candidates for
each set may be proportional to the N/L values of each set. In this
case, if the same N/L values are achieved in individual sets, the
BD candidate may be evenly distributed to the individual sets.
[0200] For example, assuming that N1=4 and L1=1 are assigned for
the set 1 and N2=8 and L2=2 are assigned for the set 2, the BD
candidate can be allocated as described above. [0201] Set 1: If
L1=1 and N1=4 are given, N1//L1=4 and (# of BD
candidate={3,3,1,1.0}) for AL={1,2,4,8,16} can be decided. [0202]
Set 2: If L2=2 and N2=8 are given, N2/L2=4 and (# of BD
candidate=0,3,3,1,11) for AL={1,2,4,8,16} can decided.
[0203] That is, since N1/L1=4 for the set 1 and N2/L2=4 for the set
2 are given, the set 1 and the set 2 may have the same number of BD
candidates. {3,3,1,1,0} is assigned to EPDCCH Set 1. and
{0,3,3,1,1} is assigned to EPDCCH Set 2 through coordination of BD
candidate allocation.
[0204] For example, assuming that N1=4 and L1=1 are assigned for
the set 1 and N2=8 and L2=1 are assigned for the set 2, the BD
candidate can be allocated as described above. In this case, the
number of BD candidate for each AL is divided in the ratio of N1/L1
to N2/L2 (i.e., the ratio of 1:2). If the division result is not
denoted by other values instead of an integer, this result is
processed by a round function. [0205] Set 1: If L1=1 and N1=4 are
given, N1//L1=4 and (# of BD candidate={2.2.1,1,0}) for
AL={1,2,4,8,16} can be decided. [0206] Set 2: If L2=1 and N2=8 are
given, N2/L2=8 and (# of BD candidate={4.4,1,1,0}) for
AL={1.2,4,8,16} can decided.
[0207] That is, assuming that N1/L1=4 of the set 1 and N2/L2=8 of
the set 2 are given, N1/L1: N2/L2=1:2 is given, the number of BD
candidates allocated to the set 2 may be double that of the number
of BD candidates allocated to the set 1.
[0208] If the BD candidate is allocated not only for one case in
which N1=4 and L1=1 are provided in consideration of N/L of the
first step from among two steps, but also for the other case in
which N2=8 and L2=2 are provided in consideration of NIL, the
following results can be obtained.
[0209] First Step--Assuming that L=L1=L2=1 is assumed for two sets,
the BD candidate for the sets is divided on the basis of N/L.
[0210] Set 1: L1=1, N1=4, # of BD candidate={2,2,1,1,0} for
AL={1,2,4,8,16} [0211] Set 2: L2=1, N2=8, # of BD
candidate={4,4,1,1,0} for AL={1,2,4.8,16}
[0212] Second Step--Correction of the Set 2 [0213] Set 1: L1=1,
N1=4, # of BD candidate={2,2,1,1,0} for AL={1,2,4,8,16} [0214] Set
2: L2=2, N2=8, # of BD candidate={0,4,4,1,1} for
AL=11,2,4,8,161
[0215] FIG. 12 is a block diagram of a transmitting device 10 and a
receiving device 20 configured to implement exemplary embodiments
of the present invention. Referring to FIG. 12, the transmitting
device 10 and the receiving device 20 respectively include radio
frequency (RF) units 13 and 23 for transmitting and receiving radio
signals carrying information, data, signals, and/or messages,
memories 12 and 22 for storing information related to communication
in a wireless communication system, and processors 11 and 21
connected operationally to the RF units 13 and 23 and the memories
12 and 22 and configured to control the memories 12 and 22 and/or
the RF units 13 and 23 so as to perform at least one of the
above-described embodiments of the present invention.
[0216] The memories 12 and 22 may store programs for processing and
control of the processors 11 and 21 and may temporarily storing
input/output information. The memories 12 and 22 may be used as
buffers. The processors 11 and 21 control the overall operation of
various modules in the transmitting device 10 or the receiving
device 20. The processors 11 and 21 may perform various control
functions to implement the present invention. The processors 11 and
21 may be controllers, microcontrollers, microprocessors, or
microcomputers. The processors 11 and 21 may be implemented by
hardware, firmware, software, or a combination thereof. In a
hardware configuration, Application Specific Integrated Circuits
(ASICs), Digital Signal Processors (DSPs), Digital Signal
Processing Devices (DSPDs), Programmable Logic Devices (PLDs), or
Field Programmable Gate Arrays (FPGAs) may be included in the
processors 11 and 21. If the present invention is implemented using
firmware or software, firmware or software may be configured to
include modules, procedures, functions, etc. performing the
functions or operations of the present invention. Firmware or
software configured to perform the present invention may be
included in the processors 11 and 21 or stored in the memories 12
and 22 so as to be driven by the processors 11 and 21.
[0217] The processor 11 of the transmitting device 10 is scheduled
from the processor 11 or a scheduler connected to the processor 11
and codes and modulates signals and/or data to be transmitted to
the outside. The coded and modulated signals and/or data are
transmitted to the RF unit 13. For example, the processor 11
converts a data stream to be transmitted into K layers through
demultiplexing, channel coding, scrambling and modulation. The
coded data stream is also referred to as a codeword and is
equivalent to a transport block which is a data block provided by a
MAC layer. One transport block (TB) is coded into one codeword and
each codeword is transmitted to the receiving device in the form of
one or more layers. For frequency up-conversion, the RF unit 13 may
include an oscillator. The RF unit 13 may include Nt (where Nt is a
positive integer) transmit antennas.
[0218] A signal processing process of the receiving device 20 is
the reverse of the signal processing process of the transmitting
device 10. Under the control of the processor 21, the RF unit 23 of
the receiving device 10 receives RF signals transmitted by the
transmitting device 10. The RF unit 23 may include Nr receive
antennas and frequency down-converts each signal received through
receive antennas into a baseband signal. The RF unit 23 may include
an oscillator for frequency down-conversion. The processor 21
decodes and demodulates the radio signals received through the
receive antennas and restores data that the transmitting device 10
wishes to transmit.
[0219] The RF units 13 and 23 include one or more antennas. An
antenna performs a function of transmitting signals processed by
the RF units 13 and 23 to the exterior or receiving radio signals
from the exterior to transfer the radio signals to the RF units 13
and 23. The antenna may also be called an antenna port. Each
antenna may correspond to one physical antenna or may be configured
by a combination of more than one physical antenna element. A
signal transmitted through each antenna cannot be decomposed by the
receiving device 20. A reference signal (RS) transmitted through an
antenna defines the corresponding antenna viewed from the receiving
device 20 and enables the receiving device 20 to perform channel
estimation for the antenna, irrespective of whether a channel is a
single RF channel from one physical antenna or a composite channel
from a plurality of physical antenna elements including the
antenna. That is, an antenna is defined such that a channel
transmitting a symbol on the antenna may be derived from the
channel transmitting another symbol on the same antenna. An RF unit
supporting a MIMO function of transmitting and receiving data using
a plurality of antennas may be connected to two or more
antennas.
[0220] In embodiments of the present invention, a UE serves as the
transmission device 10 on uplink and as the receiving device 20 on
downlink. In embodiments of the present invention, an eNB serves as
the receiving device 20 on uplink and as the transmission device 10
on downlink.
[0221] The transmitting device 10 and/or the receiving device 20
may be configured as a combination of one or more embodiments of
the present invention.
[0222] The detailed description of the exemplary embodiments of the
present invention has been given to enable those skilled in the art
to implement and practice the invention. Although the invention has
been described with reference to the exemplary embodiments, those
skilled in the art will appreciate that various modifications and
variations can be made in the present invention without departing
from the spirit or scope of the invention described in the appended
claims. For example, those skilled in the art may use each
construction described in the above embodiments in combination with
each other. Accordingly, the invention should not be limited to the
specific embodiments described herein, but should be accorded the
broadest scope consistent with the principles and novel features
disclosed herein.
[0223] The present invention can be used for wireless communication
systems such as a UE, a relay, an eNB, etc.
* * * * *